1. Field of the Invention
Certain embodiments of this invention relate to stents, urology, and treatment for benign prostate hypertrophy or prostate cancer, as well as methods for correction of vessel occlusions.
2. Description of the Related Art
Prostate enlargement, also known as benign prostate hyperplasia or benign prostate hypertrophy, is a common affliction among older men. The condition involves swelling of the prostate. The prostate surrounds the urethra, or urinary tract, and swelling of the prostate prevents passage of urine from the bladder. Benign prostate hyperplasia is uncomfortable because it makes urination difficult or impossible. The condition is also dangerous because it can lead to infection of the bladder and kidneys, and severe cases may lead to death.
Prostate cancer is also a common affliction among older men, and may lead to many of the same symptoms as benign prostate enlargement. Prostate cancer is more dangerous in that it may spread to other organs and is often fatal. Early treatment can reduce the risks of death due to prostate cancer.
A surgical cure for prostate enlargement is called resection. Resection can be accomplished by cutting away a large portion of the prostate gland. The operation can be performed by cutting through the skin to expose the prostate gland, and using scalpels to cut into the prostate. Preferably, resection is accomplished from inside the urethra, using a resectoscope inserted through the penis. The resectoscope includes an endoscope for visual observation and a resecting loop which a surgeon uses to scrape and gouge away the prostate gland from the inside.
Prostate enlargement can be treated with heat treatment such as hyperthermia or thermotherapy, cold treatment (hypothermia or cryotherapy), and ablation. It has long been known that heating a swollen prostate gland can lead to a decrease in swelling and eventual relief from the condition. Heat treatment denaturizes the proteins in the prostate tissue, like a slow cooking of the tissues. The biological effects of heat treatment and the appropriate thermal dosage are discussed in more detail in articles such as Terai, et al., Transurethral Microwave Thermotherapy For Benign Prostatic Hyperplasia, International Journal of Urology 24 (March 1995) and Pow-Sang, et al., Thermocoagulation Effect Of Diode Laser Radiation In The Human Prostate, 45 Urology 790 (May 1995), but it is sufficient for the purposes of this disclosure to understand that application of heat at sufficiently high temperature for sufficient lengths of time to destroy some or all cells in a portion of the prostate gland eventually produces a therapeutic effect.
Devices for heating the prostate are illustrated, for example, in Edwards, et al., Medical Probe Device and Method, U.S. Pat. No. 5,366,490 (Nov. 22, 1994), the entirety of which is hereby incorporated by reference, which shows a device for application of RF or microwave energy into the prostate while protecting the prostatic urethra from damage during the treatment. Hyperthermia treatment, as the term is generally used, is accomplished in the temperature range of 40xc2x0-60xc2x0 C. Thermotherapy, as the term is generally used, is accomplished by heating the prostate above 60xc2x0 C. Both heat treatments have been beneficially used in the treatment of prostate enlargement.
After heat treatment, the prostate gland will be partially destroyed. Thermal necrosis, thermocoagulation, denaturization, and other such terms are used to describe the thermal damage done to the prostate gland. The prostatic urethra will also be partially destroyed. The prostate gland and the prostatic urethra swell in response to the burn caused by the heat treatment, and this immediately causes acute blockage of the urethra. The prostate gland and prostatic urethra eventually heal, over several weeks or months, typically about three months after heat treatment.
During the healing period, much of the prostate and prostatic urethra that were damaged by the heat treatment are reabsorbed by the body through the blood vessels supplying the area. However, significant portions near the urethra slough off the urethra wall and fall into the urethra. Sloughing causes acute blockage of the urethra. Thus, during the post-operative healing period, swelling and sloughing cause acute blockage of the urethra, leading to extreme discomfort and clinical danger to the patient. After healing, the prostate will be smaller than before heat treatment and will not force closure of the urethra. The condition of benign prostate hyperplasia is essentially cured. Prostate cancer can also be treated successfully with similar heat treatments, usually in combination with chemotherapy or radiation treatment.
It has recently been proposed to use stents to support the urethra and keep it open despite pressure from the swollen prostate. The Prostacoil(trademark) temporary intraprostatic stent, marketed by Instent, Inc. of Eden Prairie, Minn., is an example of a stent adapted for use in the prostatic urethra. The stent includes an anchoring section and a prostatic section, and is placed with a delivery catheter shaft through the urethra. The stent is used long-term, for patients temporarily or permanently unfit for surgery.
A wide variety of stents have been proposed for use in various applications. Intravascular stents and coronary stents such as the Palmaz-Schatz stent illustrated in Palmaz, have been used to treat occlusions of blood vessels. A commonly suggested material for making stents is pseudoelastic and/or shape memory alloys such as nitinol. For example, Sugita, Catheter, U.S. Pat. No. 4,969,890 (Nov. 13, 1990), the entirety of which is hereby incorporated by reference, proposes use of a shape memory alloy for an intravascular stent, and shows a device for percutaneous delivery of the stent to an occluded stenotic region of a blood vessel.
Harada, et al, Method of Implanting a Stent Within a Tubular Organ of a Living Body and of Removing Same, U.S. Pat. No. 5,037,427 (Aug. 4, 1991), the entirety of which is hereby incorporated by reference, proposes use of a two-way shape memory alloy stent in a blood vessel. Two-way shape memory is useful in a stent, according to Harada, to allow removal of the stent. As explained in Harada, it is not possible to remove a one-way shape memory stent after implantation. Harada proposes use of a two-way shape memory stent with a hot, large diameter shape which holds a blood vessel open and a cold, small diameter shape which can be moved within the vessel and removed. Harada also discloses a device for percutaneous placement of the stent.
Dotter, Transluminally Placed Expandable Graft Prosthesis, U.S. Pat. No. 4,503,569, the entirety of which is hereby incorporated by reference, shows the use of a shape memory alloy stent proposed for use in blood vessels. Each of these references use saline solution injected through a catheter to control the temperature of the stent, thereby controlling the shape of the stent.
Stents may be left in blood vessels permanently, and are usually implanted for permanent use. The risk of infection around the stent in a blood vessel, or movement of the stent within a blood vessel, are somewhat limited by the environment. In the urethra, however, the risk of infection is high, and movement within the urethra may be caused by urination or ejaculation, especially if the prostate gland shrinks in response to treatment. Thus, there is a limit to the amount of time a stent may be left implanted in the urethra before infection sets in or migration occurs.
As discussed above, both prostate enlargement and prostate cancer can be treated with heat treatments such as hyperthermia or thermotherapy. As described in U.S. Pat. No. 5,830,179, the entirety of which is hereby incorporated by reference, a stent serves the dual purpose of acting as a heat source for the thermotherapy procedures, as well as acting to hold the urethra open after therapy to prevent blockage due to swelling and prostate tissue sloughing. A stent may be implanted as an interim solution to hold open the urethra while the patient awaits more aggressive surgery or treatment.
A stent may be implanted after hypothermia or cryosurgery to keep the urethra open while enlargement subsides. Finally, a stent may be implanted as a primary treatment. When the stent is implanted for any of these reasons, it is usually better to leave the bladder neck sphincter and the external sphincter unblocked by the stent. These sphincters control the flow of urine through the urethra, and if the stent is placed within these sphincters they will not be able to close. This would leave the patient incontinent. To ensure the proper positioning of the stent, the devices below provide several benefits including controlled release of the stent, tentative initial opening of the stent, and visualization of the bladder and prostatic urethra during placement.
McNamara, et al., Nitinol Stent For Hollow Body Conduits, U.S. Pat. No. 5,147,370 (Sep. 15, 1992), the entirety of which is hereby incorporated by reference, describes a catheter delivery system which uses a single pullwire to retain and release a stent wrapped on the distal end of a catheter. The stent must be provided with xe2x80x9cretaining meansxe2x80x9d in the form of pigtails or hooks on the stent ends capable of engaging a pullwire. The catheter must have two holes communicating into a lumen within the catheter, and the stent ends must enter the lumen through the holes. The pullwire is in the lumen, and engages the stent ends which enter the lumen. After release into the lumen, the retaining means are left to hang in the body lumen. This could lead to thrombus formation in blood vessels and undesirable deposition in urethral stents unless addition precautions are taken to avoid the complications. While materials may be developed in which the stent retaining pigtail structures are not set into the form of the stent, common stent alloys such as Elgiloy, nitinol and stainless steel will take a set in the form of pigtails if deformed as suggested by McNamara.
Hillstead, Apparatus And Method For Placement Of A Stent Within A Subject Vessel, U.S. Pat. No. 4,913,141 (Apr. 3, 1990), the entirety of which is hereby incorporated by reference, discloses a stent delivery device which uses a pullwire running through the central lumen of the catheter and exiting the catheter to run over the stent ends. The stent is deployed by pulling the pullwire proximally, requiring the pullwire to course over intimal and endothelial surfaces of the body lumen to be treated. This could lead to damage of lumenal surfaces and attendant healing responses which are undesirable. Neither McNamara nor Hillstead provide a mechanism which permits retention and release of the stent with a mechanism which remains in the annular space of the stent, and do not present radially extending features such as the radially outwardly protruding pullwires or radially inwardly protruding pigtails.
Othel-Jacobsen, Segmentarily Expandable Tubular Endoluminal Prosthesis, PCT Application No. PCT/DK93/00015, published Jul. 22, 1993 (WO 93/13824), the entirety of which is incorporated by reference, shows a stent which has a primary shape with one or more segments having a diameter which is considerably greater than the rest of the stent. Each segment of the stent has a substantially constant diameter. The larger segments of the stent allow for fastening of the stent inside a natural cavity. However, among other disadvantages, the particular shape of the stent is not always effective in retaining the stent inside the cavity.
The devices described below include urological stents and devices for placing the stents in the urethra. Methods for treating benign prostate hyperplasia or prostate cancer with heat treatment, either hyperthermia or thermotherapy, using the stent as the heat source, are also described. Also, fabrication of the stent from a nitinol alloy, shape memory alloy, or pseudoelastic alloy, permits easy placement and subsequent removal of the stent, so that the stent may be placed in the urethra during the healing period and removed when no longer necessary. The inventions disclosed and claimed below combine various aspects of treatments discussed above and various new concepts to create new devices and methods for treating benign prostate hyperplasia.
Stent delivery systems described below permit placement of stents in the urethra and other body vessels. The devices are intended to deploy a shape memory stent or other resilient stent into the prostatic urethra under direct vision. The surgeons who use the stent delivery systems can easily place the stent within the prostatic urethra and make sure that the stent does not block the bladder neck sphincter.
In one embodiment, the stent is retained on the catheter with one or more retaining wires or rods which engage the stent ends. The catheter is comprised of two coaxial tubes, one inside the other, and the distal end of the stent is secured to the inner tube while the proximal end of the stent is secured to the outer tube. When both ends of the stent are secured to their respective tubes, the tubes may be rotated relative to each other to open the stent or tighten the stent. The stent may be released from the catheter by pulling the pullwires proximally out of engagement with the stent ends. The pullwire which retains the distal end of the stent may be released first, and the location of the distal end of the stent is observed. Once the distal end of the stent is located properly, the proximal end of the stent may be released from the catheter by pulling the pullwire which retains the proximal end of the stent out of engagement with the proximal end of the stent.
In another embodiment, a stent delivery device includes an inner tube and an outer tube. The inner tube has a distal end releasably connectable to the first end of the stent. The outer tube is rotatably slidable over the inner tube and has a distal end releasably connectable to the second end of the stent. In one embodiment, a sheath is provided which is slideable over the outer tube. A trigger may also be provided which is operably connected to the sheath for moving the sheath along the outer tube. In another embodiment, a belt is operably connected to the outer tube for rotating the outer tube relative to the inner tube. The stent may be releasably connectable to the first and second ends of the stent using at least one pullwire.
In accordance with a further aspect of the present invention, there is provided a stent deployment device. The device comprises a tubular body, having a proximal end and a distal end, the tubular body comprising a first and a second stent support. A hand piece is provided on the proximal end of the tubular body. A first control is provided on the hand piece, for manipulating the first stent support, and a second control is provided on the hand piece for manipulating the second stent support.
In one embodiment, the first stent support comprises an outer tubular sleeve for surrounding the stent. The first control comprises a control for proximally retracting the first stent support, to expose at least a portion of the stent. The first control may comprise a slider switch or lever, such as a trigger.
The second stent support may comprise a tubular body, which is releasably connected to at least a first end of the stent. The second control may comprise a control for rotating the second stent support. In one embodiment, the second control comprises a belt which is wrapped around the second stent support. Lateral retraction of the belt causes a commensurate rotation of the second stent support.
Preferably, the first and second stent supports are concentric tubes, and the stent deployment device further comprises a third stent support, comprising a third tube such that the third stent support forms an inner tube which carries the stent and is releasably connected to a distal end of the stent. The second stent support comprises an intermediate tube, concentrically carried by the inner tube, and releasably secured to a proximal end of the stent. The first stent support comprises an outer tube, concentrically carried by the intermediate tube, for covering the stent during transluminal positioning of the stent deployment device.
Preferably, the third stent support comprises an inside diameter which is greater than the outside diameter of an optical visualization device such as an endoscope which is releasably mounted to the stent deployment device, thereby forming an annular lumen extending distally through the tubular body. An infusion port may be provided on the hand piece, for communication with the annular lumen, to permit infusion of fluid media through the tubular body and out of the distal end thereof.
In another embodiment of the present invention, a stent for use within the prostatic urethra is provided. The stent comprises a length of wire having a substantially helical configuration and being expandable between a collapsed shape and an expanded shape. The expanded shape includes a proximal end and a distal end and a substantially cylindrical portion extending from the distal end toward the proximal end. The expanded shape also includes an enlarged region proximal of the cylindrical portion wherein an outer diameter of the enlarged region progressively increases toward the proximal end.
In another embodiment of the present invention, a method for delivering a stent into the prostatic urethra of a patient is provided. A length of wire is provided having a substantially helical configuration which is expandable between a collapsed shape and an expanded shape. The expanded shape includes a proximal end and a distal end and a substantially cylindrical portion extending from the distal end toward the proximal end. The expanded shape also includes an enlarged region proximal of the cylindrical portion wherein an outer diameter of the enlarged region progressively increases toward the proximal end. The stent is delivered in its collapsed shape into the prostatic urethra of the patient. The stent is expanded to its expanded shape within the prostatic urethra of the patient. The proximal end of the stent is located relatively closer to the external sphincter and the distal end of the stent is located relatively closer to the bladder neck sphincter.
Further features and advantages of the present invention will become apparent from the detailed description of preferred embodiments which follows, when considered together with the attached drawings and claims.